The present invention relates, in general, to memory devices and, more particularly, to nonvolatile memory devices.
Electrically Erasable Programmable Read Only Memory (EEPROM) permits storing data that can be retained even if power to the memory is removed. An EEPROM cell stores data by storing electrical charge in an electrically isolated floating gate of a field effect transistor (FET). The stored electrical charge controls the threshold of the FET, thereby controlling the memory state of the EEPROM cell.
Two common structures for an EEPROM cell are a double poly structure and a single poly structure. The double poly structure is conventionally fabricated using two polycrystalline silicon layers. The single poly structure requires only one polycrystalline silicon layer and, therefore, is simpler and less expensive to fabricate than the double poly structure. However, the single poly structure usually requires more silicon area than the double poly structure.
To read data from the EEPROM cell, a sense amplifier is conventionally used to sense a current flowing in the FET, thereby determining the memory state of the EEPROM cell. However, the sense amplifier increases the circuit complexity, silicon area, and fabrication cost of the EEPROM cell. In addition, the sense amplifier consumes a large current during the process of reading data from the EEPROM cell and, therefore, is power inefficient.
Accordingly, it would be advantageous to have a nonvolatile memory device and a method for accessing the nonvolatile memory device. It is desirable for the nonvolatile memory device to be simple and inexpensive to fabricate. It is also desirable for the accessing method to be energy efficient. It would be of further advantage for the nonvolatile memory device to be reliable.